A MEMS device includes at least one mechanical element, such as a sensor, actuator, or resonator that is formed using a micromachining process that selectively etches away parts of a wafer. The wafer may include added structural layers and may be made of a semiconductor material, such as silicon. By using a semiconductor wafer, standard foundry integrated circuit (IC) processing, such as complementary metal-oxide-semiconductor (CMOS), bipolar, and bipolar CMOS (BICMOS) may be used to add electronic components, which form an IC, to create a combined MEMS device and IC on a single wafer, which includes both mechanical elements and electronic components. However, MEMS devices may be formed before or after standard foundry IC processing using high temperature oxidation, deposition, or both. Such pre-processing and post-processing steps add complexity and cost. Further, some MEMS devices, such as resonators, may require very fine gaps, which are difficult to fabricate.
Incorporating a MEMS device and an IC on a single wafer using standard foundry IC processing techniques eliminates the need for very fine gaps, therefore simplifying the manufacturing process as well as minimizing the overall footprint of the semiconductor device. However, a common challenge remaining in creating a MEMS resonator device is the inability to construct transducers that will efficiently and effectively convert electrical signals to mechanical vibrations and vice versa. The transducers are effectively capacitors created by forming a dielectric plate between a transducer plate and the body of the MEMS device. To increase the effectiveness of the transducers, there is a need to increase capacitance by minimizing the distance between the transducer plate and the body as well as provide a dielectric plate with a relatively high dielectric constant without significantly increasing the cost or complexity of the manufacturing process.
Accordingly, there is a need for a process to create a MEMS device using a standard CMOS process. There is a further need to increase the efficiency of the transducers of the MEMS device using such a process.